With the increasing emphasis on packages, mail, and other such items having to arrive at its location “overnight”, more and more cargo is being shipped by aircraft 100 (See FIG. 1). While some aircraft are configured to transport cargo only, others are configured to transport both passengers and cargo.
Typically, the items being shipped are first loaded onto pallets, containers, or the like. In the airfreight industry, any one of these various categories of devices is referred to as a Unit Load Device 102 (ULD). Within each category, the ULDs come in various sizes, shapes and capacities and bear markings 104 that identify their type, maximum gross weight and tare weight, among other characteristics.
This initial task of placing the items to be shipped into a ULD may be performed at a location away from the immediate vicinity of the aircraft. In due course, however, the ULD is weighed, brought to the aircraft and sent up a ramp 106, scissors lift, or other means and then through a doorway 108. Once inside, the ULD is moved about the cargo compartment until it reaches its final position for the flight. As depicted in FIG. 2, on any given flight, a cargo aircraft 200 can carry a number of ULDs 202, of which aforementioned ULD 102 may be just one example, and so additional ULDs are brought onboard and placed in their proper positions. In certain aircraft, not all ULDs are in the same compartment, some being placed in the forward compartment 204 while others being placed in the aft compartment 206. And, as seen in the forward compartment 204, even ULDs of the same type need not necessarily all be adjacent to one another. Also, in many aircraft, ULDs may be placed on different vertical levels, or decks.
To facilitate moving around the ULD within the cargo compartment, the floor of the cargo compartment is provided with a number of structures with raised surfaces. These structures may take the form of parallel roller tracks arranged longitudinally along the length of the cargo floor, ball panel units, and the like. The bottom surface of the ULD rides on the raised surfaces provided by the rollers and balls of these structures, as it is moved within the compartment.
Once moved to its final position, further movement of the ULD is prevented for duration of the flight. This is done to ensure that the ULD will not move about when the aircraft is subjected to rough air, vibrations, acceleration, deceleration, and rough landings. To prevent movement of the ULD in flight, the floor and side walls of the cargo compartment may be provided with restraints that serve to keep the ULD stationary.
One example of such a restraint is a latch that is removably fixed to the floor and selectively adjustable between a deployed position and a retracted position. In the deployed position, an engaging member of the latch is erect and rises above the upper surface of the rollers, whereby it can confine movement of the ULD. In the retracted position, the engaging member is recessed, below the upper surface of the rollers so that the ULD can pass over it. The latch itself may be moved between the deployed and retracted positions simply by stepping on it or pressing a switch. Such latches are known in the art, and come in different types and sizes. The latches are positioned at predetermined “install points” on the cargo floor, the install points simply being defined as locations where there are holes, cutouts or other fixtures suitable for installing a latch. One example of such an install point may be between the rails of a roller track, another may be along a side rail on a wall of the cargo compartment.
A cargo floor may be provided with several hundred install points. However, not all install points are populated with restraints, due to the weight and cost of the latter. For example, on a cargo floor having 800 install points, perhaps 300 or so of these might be fitted with restraints. Usually, the operator of the aircraft will consider the types of ULDs they are likely to use, along with the likely load configurations, i.e., the various permutations in which different numbers and types of ULDs would be placed, and install a number of restraints accordingly.
FIG. 2 depicts a sample restraint configuration chart 250 of a cargo floor. This chart has a numbered grid 252 to establish an X-Y frame of reference for identifying locations on the cargo floor. Various restraints are indicated by symbols 254 and legend 256 is provided to identify the type of restraint associated with each symbol.
Each ULD normally requires multiple restraints, and different types of ULDs require different numbers of restraints. Operational criteria for each ULD specify the required number of restraints to be used, and the locations of those restraints relative to the ULD for when the ULD is at its maximum gross weight. They also specify a reduced maximum gross weight for when one or more of the required number of restraints is missing. Thus, on a given flight, if one of several restraints to be used to secure a ULD is damaged or missing, that ULD may still be transported in the chosen position, but only if it meets the reduced maximum gross weight specification.
The number of ULDs, the types of ULDs to be carried, and the weight of each ULD can change from flight to flight. Great care must be taken when loading aircraft with cargo to assure that the weight and balance of the aircraft with the loaded cargo is acceptable. Aircraft performance and handling characteristics are affected by the gross weight and center of gravity limits. An overloaded or improperly balanced aircraft will require more power and greater fuel consumption to maintain flight, and the stability and controllability may be seriously affected. Lack of appreciation for the effects of weight and balance on the performance of aircraft, particularly in combination with such performance reducing factors as high density altitude, frost or ice on the wings, low engine power, severe or uncoordinated maneuvers, and emergency situations, can be a prime factor in aircraft accidents.
Before the ULDs are loaded, the load master, or other cognizant individual, develops a desired load configuration that takes into account the weight and balance criteria, and the number, types and weights of the ULDs. This desired load configuration indicates where, on the cargo floor, each of the ULDs to be loaded onto the aircraft, should be positioned. In its simplest form, then, the desired load configuration is simply a two-column list, the first column identifying each ULD and the second its corresponding desired position.
The loading crew tasked with loading the aircraft receives a print out of the desired load configuration. But before loading the ULDs onto the aircraft, a ground member must establish that restraints of the correct type are installed at the various install points. This is done to ensure that each ULD's operational requirements for being secured by restraints can be met. For this, the loading crew member, armed with the desired load configuration, and relying on his or her familiarity with various ULDs, restraints and cargo floor equipment and assisted by color-coded markings on the cargo floor designating install points and the like, performs a visual inspection, and determines whether operable restraints of the correct types are installed in the correct locations for each of the ULDs to be loaded onto the aircraft.
During the inspection process, the loading crew member may discover a missing, damaged, or inoperable restraint. In such case, he or she reports this to the load master or other cognizant individual, who then may check the ULD operational criteria to determine whether either a lighter weight ULD or a different type of ULD could be located in that position, instead of leaving the position unused. Sometimes, it may be possible to move a restraint from one install point where it will not be needed for the upcoming flight, to another install point having a missing or damaged restraint, so that the ULD restraints requirements will be satisfied.